Match the disorders in List I with their causes in List II and...

Thalassemia is a quantitative blood disorder that results in the synthesis of too few globin molecules. Thus, (A) matches (III).

Sickle-cell anaemia is a qualitative blood disorder that results in the synthesis of an incorrectly functioning globin molecule. Thus, (B) matches (IV).

Turner's Syndrome is caused by the absence of one of the X chromosomes (45$with$X0$), which occurs due to the non-disjunction of sex chromosomes during gametogenesis. Thus, (C) matches (I).<br><br>Down's Syndrome is caused by the presence of an additional copy of chromosome number 21$ (trisomy of $21$), which occurs due to the non-disjunction of the $21$st pair of chromosomes. Thus, (D) matches (II).

The correct matching is (A) - (III), (B) - (IV), (C) - (I), (D) - (II).

Answer: (A) - (III), (B) - (IV), (C) - (I), (D) - (II).